Exhaust assembly for a plasma processing system

ABSTRACT

An exhaust assembly is described for use in a plasma processing system, whereby secondary plasma is formed in the exhaust assembly between the processing space and chamber exhaust ports in order to reduce plasma leakage to a vacuum pumping system, or improve the uniformity of the processing plasma, or both. The exhaust assembly includes a powered exhaust plate in combination with a ground electrode is utilized to form the secondary plasma surrounding a peripheral edge of a substrate treated in the plasma processing system.

This application is a Divisional of U.S. patent application Ser. No.11/464,003, filed on Aug. 11, 2006, the entirety of which is herebyincorporated by reference herein.

FIELD OF INVENTION

The present invention relates to a method and apparatus for plasmaprocessing a substrate, and more particularly to a method and system foroperating a processing system to adjust the spatial uniformity of aprocessing plasma.

DESCRIPTION OF RELATED ART

During semiconductor processing, a (dry) plasma etch process can beutilized to remove or etch material along fine lines or within vias orcontacts that are patterned on a silicon substrate. The plasma etchprocess generally involves positioning in a processing chamber asemiconductor substrate having an overlying patterned, protective layer,for example a photoresist layer. Once the substrate is positioned withinthe chamber, an ionizable, dissociative gas mixture is introduced intothe chamber at a pre-specified flow rate, while a vacuum pump isthrottled to achieve an ambient process pressure.

Thereafter, a plasma is formed when a fraction of the gas speciespresent is ionized by electrons heated via the transfer of radiofrequency (RF) power, either inductively or capacitively, or microwavepower using, for example, electron cyclotron resonance (ECR). Moreover,the heated electrons serve to dissociate some species of the ambient gasspecies and create reactant specie(s) suitable for the exposed surfaceetch chemistry. Once the plasma is formed, selected surfaces of thesubstrate are etched by the plasma. The process is adjusted to achieveappropriate conditions, including an appropriate concentration ofdesirable reactant and ion populations to etch various features (e.g.,trenches, vias, contacts, etc.) in the selected regions of thesubstrate. Such substrate materials where etching is required, include,for example, silicon dioxide (SiO₂), low-k dielectric materials,poly-silicon, and silicon nitride.

SUMMARY OF THE INVENTION

According to principles of the invention, a method and system areprovided that include operating a processing apparatus to reduce leakageof processing plasma to a vacuum pumping system of the processingapparatus.

According to certain embodiments of the invention, an exhaust assemblyof the processing apparatus is operated to reduce leakage of the plasmato the vacuum pumping system.

According to other embodiments of the invention, a method and system aredescribed for operating an exhaust system of the processing apparatus toadjust the spatial uniformity of the processing plasma utilized to treatthe substrate.

According to still other embodiments of the invention, a method fortreating a substrate is provided, and a computer readable medium isprovided with program instructions to cause a computer system to controla plasma processing system according to the method.

According to certain described embodiments of the invention, a method isprovided that comprises: disposing said substrate on a substrate holderin a plasma processing chamber; forming a processing plasma in a processspace above and adjacent said substrate using a plasma generation systemcoupled to said plasma processing chamber; disposing an exhaust assemblywithin said plasma processing chamber such that said exhaust assemblysubstantially surrounds said substrate holder and separates said processspace from a pumping space coupled to a vacuum pumping system; couplingelectrical power to said exhaust assembly thereby forming a secondaryplasma in order to alter said processing plasma; and exposing saidsubstrate to said altered processing plasma.

According to other described embodiments of the invention, a plasmaprocessing system configured to process a substrate with plasma isprovided comprising a plasma processing chamber configured to facilitatethe formation of a processing plasma; a substrate holder coupled to saidplasma processing chamber and configured to support said substrate; aplasma generation system coupled to said plasma processing chamber andconfigured to form said processing plasma from a process gas in aprocess space adjacent said substrate; a vacuum pumping system coupledto said plasma processing chamber and configured to evacuate saidprocess gas; an exhaust assembly coupled to said plasma processingchamber around said substrate holder and separating said process spacefrom a pumping space coupled to said vacuum pumping system; and anelectrical power source coupled to said exhaust assembly and configuredto form a secondary plasma in order to alter said processing plasma.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A presents a schematic representation of a plasma processingsystem of the prior art;

FIG. 1B presents a cross-sectional plan view along line 1B-1B of FIG. 1Aof the exhaust assembly for the plasma processing system depicted inFIG. 1A;

FIG. 1C presents a cross-sectional plan view along line 1C-1C of FIG. 1Aof the pumping port for the plasma processing system depicted in FIG.1A;

FIG. 2 presents a schematic representation of a plasma processing systemhaving an exhaust assembly according to an embodiment of the invention;

FIG. 3 presents a schematic representation of a plasma processing systemhaving an exhaust assembly according to another embodiment of theinvention;

FIG. 4 shows a schematic diagram of a plasma processing system accordingto an embodiment of the invention;

FIG. 5 shows a schematic diagram of a plasma processing system accordingto another embodiment of the invention;

FIG. 6 shows a schematic diagram of a plasma processing system accordingto another embodiment of the invention;

FIG. 7 shows a schematic diagram of a plasma processing system accordingto another embodiment of the invention;

FIG. 8 shows a schematic diagram of a plasma processing system accordingto another embodiment of the invention; and

FIG. 9 illustrates a method of treating a substrate using plasmaaccording to certain embodiments of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, for purposes of explanation and notlimitation, specific details are set forth, such as a particulargeometry of the plasma processing system and descriptions of variousprocesses. However, it should be understood that the invention may bepracticed in other embodiments that depart from these specific details.

In material processing methodologies, pattern etching comprises theapplication of a thin layer of light-sensitive material, such asphotoresist, to an upper surface of a substrate that is subsequentlypatterned in order to provide a mask for transferring this pattern tothe underlying thin film on a substrate during etching. The patterningof the light-sensitive material generally involves exposure by aradiation source through a reticle (and associated optics) of thelight-sensitive material using, for example, a micro-lithography system,followed by the removal of the irradiated regions of the light-sensitivematerial (as in the case of positive photoresist), or non-irradiatedregions (as in the case of negative resist) using a developing solvent.Moreover, this mask layer may comprise multiple sub-layers.

During pattern etching, a dry plasma etching process is often utilized,wherein plasma is formed from a process gas by coupling electromagnetic(EM) energy, such as radio frequency (RF) power, to the process gas inorder to heat electrons and cause subsequent ionization and dissociationof the atomic and/or molecular composition of the process gas.Furthermore, an optional (negative) direct current (DC) voltage can becoupled to the plasma processing system in order to create a ballisticelectron beam that strikes the substrate surface during a fraction ofthe RF cycle, i.e., the positive half-cycle of the coupled RF power. Ithas been observed that the ballistic electron beam can enhance theproperties of the dry plasma etching process by, for example, improvingthe etch selectivity between the underlying thin film (to be etched) andthe mask layer, reducing charging damage such as electron shadingdamage, etc. Additional details regarding the generation of a ballisticelectron beam are disclosed in pending U.S. patent application Ser. No.11/156,559, entitled “Plasma processing apparatus and method” andpublished as US patent application no. 2006/0037701 A1; the entirecontents of which are herein incorporated by reference in theirentirety.

While the properties of the plasma and associated chemistry as well asthe properties of the optional ballistic electron beam are important,the spatial uniformity of the plasma properties is also very important.Due to the difference in mobility between electrons and ions, which arerespectively relatively more and less mobile, a plasma sheath forms onsurfaces bounding the plasma and a plasma potential greater than that ofthe boundary surfaces forms for the bulk plasma. As a result, the plasmadiffuses throughout the plasma volume seeking such ground surfaces.

In order to counter the diffusion of plasma to systems susceptible toplasma damage, such as the vacuum pumping system, devices are utilizedto confine the plasma to the processing space proximate the substrate.For example, an exhaust assembly consisting of an electrically groundedbaffle plate has been used for such a purpose. Referring now to FIG. 1A,a schematic illustration of a plasma processing system 10 incorporatinga conventional baffle plate is presented. The plasma processing system10 comprises a plasma processing chamber 14 configured to facilitate theformation of a processing plasma in process space 15, a substrate holder12 coupled to the plasma processing chamber 14 and configured to supportsubstrate 25, and a vacuum pumping system 16 coupled to the plasmaprocessing chamber 14 and configured to evacuate process space 15through vacuum pumping port 19.

Additionally, the plasma processing system 10 comprises an exhaustassembly 17 consisting of a baffle plate 17 a with a plurality ofopenings 27 to allow the passage of process gases there-through fromprocess space 15 to vacuum pumping system 16 (see FIG. 1B). In order topermit the coupling of various utility connections to substrate holder12, the vacuum pumping port 19 does not extend entirely around theperimeter of substrate holder 12. As shown in FIG. 1C, the vacuumpumping port 19 can include three openings 19 a, 19 b, 19 c, throughwhich process gases pass on to a vacuum pump.

The use of the baffle plate 17 a is intended to relieve the processspace 15 of pressure non-uniformity due to the asymmetric pumping.Moreover, the use of the baffle plate 17 a is intended to reduce theleakage of plasma from process space 15 to vacuum pumping system 16.However, the inventor has observed an asymmetry in the leakage 18 ofplasma from process space 15 through the exhaust assembly 17 due to theasymmetry of the vacuum pumping port 19. As a result, non-uniformtreatment of substrate 25 is observed as well as excessive plasmaleakage to vacuum pumping system 16. One approach to reduce the observedplasma leakage is to reduce the diameter of the openings in the baffleplate 17 a. However, this reduction is performed at the expense of theflow conductance through the baffle plate, thus dramatically reducingthe ability to deliver a desired pumping speed to the process space 15.

Referring now to FIG. 2, a processing system 100 and an exhaust assemblytherefor are provided according to an embodiment of the invention. Aplasma processing system 100 is illustrated comprising a plasmaprocessing chamber 110 configured to facilitate the formation of plasmain a process space 115, a substrate holder 120 coupled to the plasmaprocessing system 110 and configured to support substrate 25, and avacuum pumping system 130 coupled to plasma processing chamber 110 viapumping port 132 and configured to evacuate process gases from processspace 115. Additionally, plasma processing system 100 comprises a plasmageneration system 160 coupled to the plasma processing chamber 110 andconfigured to form processing plasma from a process gas in process space115.

The plasma generation system 160 may comprise one or more of acapacitively coupled plasma (CCP) system, an inductively coupled plasma(ICP) system, a transformer coupled plasma (TCP) system, an electroncyclotron resonance (ECR) plasma system, a helicon wave plasma system, asurface wave plasma system, or a slotted plane antenna (SPA) plasmasystem, or a combination of two or more thereof. Each plasma systemdescribed above is well known to those skilled in the art.

Referring still to FIG. 2, plasma processing system 100 furthercomprises an exhaust assembly 140 configured to generate a secondaryplasma. Exhaust assembly 140 comprises a first exhaust plate 142 coupledto a power source 150, a second exhaust plate 144 coupled to electricalground, and electrical insulation rings 146 configured to electricallyinsulate the first exhaust plate from substrate holder 120 and the(electrically grounded) walls of process chamber 110. As illustrated inFIG. 2, the first and second exhaust plates 142, 144 surround substrateholder 120 and form the secondary plasma there-between.

Power source 150 can include a direct current (DC) electrical powersource or an alternating current (AC) electrical power source. Forexample, power source 150 can include a radio frequency (RF) powersource configured to couple RF power to the first exhaust plate 142.

The first exhaust plate 142 and the second exhaust plate 144 can befabricated from a metal, such as aluminum or anodized aluminum.Additionally, the first exhaust plate 142 and the second exhaust plate144 can be coated with a ceramic, such as aluminum oxide or yttriumoxide. For example, each exhaust plate may be coated with a materialselected from the group consisting of Al₂O₃, Sc₂O₃, Sc₂F₃, YF₃, La₂O₃,Y₂O₃, and DyO₃.

Referring still to FIG. 2, plasma processing system 100 furthercomprises a controller 170 coupled to plasma processing chamber 110,substrate holder 120, plasma generation system 160, power system 150 andvacuum pumping system 130, and configured to exchange data with each ofthese components in order to execute a process within the plasmaprocessing chamber 110 to treat substrate 25.

Referring now to FIG. 3, a processing system 300 and an exhaust assemblytherefor are provided according to another embodiment of the invention.A plasma processing system 200 is illustrated comprising an exhaustassembly 240 configured to generate secondary plasma about the peripheryof substrate holder 120. Plasma processing system 200 comprises similarcomponents as described in FIG. 2, wherein like reference numeralsdesignate identical or corresponding parts. The exhaust assembly 240comprises a first exhaust plate 242 coupled to power source 150, aground electrode 244 coupled to an outer wall of process chamber 110,and electrical insulator rings 246 configured to electrically insulatethe first exhaust plate 242 from substrate holder 120 and the(electrically grounded) walls of process chamber 110. Additionally,exhaust assembly 240 can include an optional second exhaust plate 248located proximate to and below the first exhaust plate 242. The secondexhaust plate 248 is fabricated from an electrically non-conductivematerial. As illustrated in FIG. 3, the first exhaust plates 242 and theground electrode 244 surround substrate holder 120 and form thesecondary plasma there-between.

The first exhaust plate 242 and the ground electrode 244 can befabricated from a metal, such as aluminum or anodized aluminum.Additionally, the first exhaust plate 242 and the ground electrode 244can be coated with a ceramic, such as aluminum oxide or yttrium oxide.For example, the exhaust plate 242 and the ground electrode 244 may becoated with a material selected from the group consisting of Al₂O₃,Sc₂O₃, Sc₂F₃, YF₃, La₂O₃, Y₂O₃, and DyO₃. The optional second exhaustplate 248 can be fabricated from a ceramic or plastic material. Forexample, the second exhaust plate 248 may be fabricated from quartz,sapphire, silicon, silicon nitride, silicon carbide, alumina, aluminumnitride, Teflon®, polyimide, etc.

FIG. 4 illustrates a plasma processing system 300 according to anotherembodiment. Plasma processing system 300 comprises a plasma processingchamber 310, substrate holder 320, upon which a substrate 25 to beprocessed is affixed, and vacuum pumping system 330. Substrate 25 can bea semiconductor substrate, a wafer or a liquid crystal display. Plasmaprocessing chamber 310 can be configured to facilitate the generation ofplasma in processing region 315 adjacent a surface of substrate 325. Anionizable gas or mixture of gases is introduced via a gas injectionsystem (not shown) and the process pressure is adjusted. For example, acontrol mechanism (not shown) can be used to throttle the vacuum pumpingsystem 30. Plasma can be utilized to create materials specific to apre-determined materials process, and/or to aid the removal of materialfrom the exposed surfaces of substrate 25. The plasma processing system300 can be configured to process a substrate of any size, such as 200 mmsubstrates, 300 mm substrates, or larger.

Substrate 25 can be affixed to the substrate holder 320 via anelectrostatic clamping system. Furthermore, substrate holder 320 canfurther include a cooling system or heating system that includes are-circulating fluid flow that receives heat from substrate holder 320and transfers heat to a heat exchanger system (not shown) when cooling,or transfers heat from the heat exchanger system to the fluid flow whenheating. Moreover, gas can be delivered to the back-side of substrate 25via a backside gas system to improve the gas-gap thermal conductancebetween substrate 25 and substrate holder 320. Such a system can beutilized when temperature control of the substrate is required atelevated or reduced temperatures. For example, the backside gas systemcan comprise a two-zone gas distribution system, wherein the backsidegas (e.g., helium) pressure can be independently varied between thecenter and the edge of substrate 25. In other embodiments,heating/cooling elements, such as resistive heating elements, orthermoelectric heaters/coolers can be included in the substrate holder320, as well as the chamber wall of the plasma processing chamber 310and any other component within the plasma processing system 300.

In the embodiment shown in FIG. 4, substrate holder 320 can comprise anelectrode through which RF power is coupled to the processing plasma inprocess space 315. For example, substrate holder 320 can be electricallybiased at a RF voltage via the transmission of RF power from a RFgenerator 340 through an optional impedance match network 342 tosubstrate holder 320. The RF bias can serve to heat electrons to formand maintain plasma, or affect the ion energy distribution functionwithin the sheath, or both. In this configuration, the system canoperate as a reactive ion etch (RIE) reactor, wherein the chamber and anupper gas injection electrode serve as ground surfaces. A typicalfrequency for the RF bias can range from 0.1 MHz to 100 MHz. RF systemsfor plasma processing are well known to those skilled in the art.

Furthermore, impedance match network 342 serves to improve the transferof RF power to plasma in plasma processing chamber 310 by reducing thereflected power. Match network topologies (e.g. L-type, π-type, T-type,etc.) and automatic control methods are well known to those skilled inthe art.

Referring still to FIG. 4, plasma processing system 300 furthercomprises an optional direct current (DC) power supply 350 coupled to anupper electrode 352 opposing substrate 25. The upper electrode 352 maycomprise an electrode plate. The electrode plate may comprise asilicon-containing electrode plate. Moreover, the electrode plate maycomprise a doped silicon electrode plate. The DC power supply caninclude a variable DC power supply. Additionally, the DC power supplycan include a bipolar DC power supply. The DC power supply 350 canfurther include a system configured to perform at least one ofmonitoring adjusting, or controlling the polarity, current, voltage, oron/off state of the DC power supply 50. Once plasma is formed, the DCpower supply 350 facilitates the formation of a ballistic electron beam.An electrical filter may be utilized to de-couple RF power from the DCpower supply 350.

For example, the DC voltage applied to electrode 352 by DC power supply350 may range from approximately −2000 volts (V) to approximately 1000V. Desirably, the absolute value of the DC voltage has a value equal toor greater than approximately 100 V, and more desirably, the absolutevalue of the DC voltage has a value equal to or greater thanapproximately 500 V. Additionally, it is desirable that the DC voltagehas a negative polarity. Furthermore, it is desirable that the DCvoltage is a negative voltage having an absolute value greater than theself-bias voltage generated on a surface of the upper electrode 352. Thesurface of the upper electrode 352 facing the substrate holder 320 maybe comprised of a silicon-containing material.

Furthermore, the amplitude of the RF power coupled to substrate holder320 can be modulated in order to affect changes in the spatialdistribution of the electron beam flux to substrate 25. Additionaldetails can be found in co-pending U.S. patent application Ser. No.11/______, entitled “Method and system for controlling the uniformity ofa ballistic electron beam by RF modulation” (Lee Chen & Ping Jiang),filed on Jul. 31, 2006; the entire contents of which are incorporated byreference in their entirety.

Referring still to FIG. 4, plasma processing system 300 furthercomprises an exhaust assembly 334 surrounding substrate holder 320 andconfigured to separate processing space 315 from pumping space 335. Theexhaust system 334 is coupled to power source 332 and configured togenerate secondary plasma to reduce plasma leakage from process space315 to pumping space 335, and improve the spatial uniformity ofprocessing plasma in process space 315. For example, the exhaustassembly 334 can include either embodiment described in FIG. 2 or 3.

Vacuum pumping system 330 can include a turbo-molecular vacuum pump(TMP) capable of a pumping speed up to 5000 liters per second (andgreater) and a gate valve for throttling the chamber pressure. Inconventional plasma processing devices utilized for dry plasma etch, a1000 to 3000 liter per second TMP can be employed. TMPs can be used forlow pressure processing, typically less than 50 mtorr. For high pressureprocessing (i.e., greater than 100 mtorr), a mechanical booster pump anddry roughing pump can be used. Furthermore, a device for monitoringchamber pressure (not shown) can be coupled to the plasma processingchamber 310. The pressure measuring device can be, for example, a Type628B Baratron absolute capacitance manometer commercially available fromMKS Instruments, Inc. (Andover, Mass.).

Referring still to FIG. 4, plasma processing system 300 furthercomprises a controller 390 that comprises a microprocessor, memory, anda digital I/O port capable of generating control voltages sufficient tocommunicate and activate inputs to plasma processing system 300 as wellas monitor outputs from plasma processing system 300. Moreover,controller 390 can be coupled to and can exchange information with RFgenerator 340, impedance match network 342, optional DC power supply350, the gas injection system (not shown), power source 332, vacuumpumping system 330, as well as the backside gas delivery system (notshown), the substrate/substrate holder temperature measurement system(not shown), and/or the electrostatic clamping system (not shown). Aprogram stored in the memory can be utilized to activate the inputs tothe aforementioned components of plasma processing system 300 accordingto a process recipe in order to perform the method of etching a thinfilm. One example of controller 390 is a DELL PRECISION WORKSTATION610™, available from Dell Corporation (Austin, Tex.).

Controller 390 may be locally located relative to the plasma processingsystem 300, or it may be remotely located relative to the plasmaprocessing system 300 via an internet or intranet. Thus, controller 390can exchange data with the plasma processing system 300 using at leastone of a direct connection, an intranet, or the internet. Controller 390may be coupled to an intranet at a customer site (i.e., a device maker,etc.), or coupled to an intranet at a vendor site (i.e., an equipmentmanufacturer). Furthermore, another computer (i.e., controller, server,etc.) can access controller 390 to exchange data via at least one of adirect connection, an intranet, or the internet.

In the embodiment shown in FIG. 5, the plasma processing system 300 canbe similar to the embodiment of FIG. 3 or 4 and further comprise eithera stationary, or mechanically or electrically rotating magnetic fieldsystem 460, in order to potentially increase plasma density and/orimprove plasma processing uniformity, in addition to those componentsdescribed with reference to FIG. 3. Moreover, controller 490 can becoupled to magnetic field system 60 in order to regulate the speed ofrotation and field strength. The design and implementation of a rotatingmagnetic field is well known to those skilled in the art.

In the embodiment shown in FIG. 6, the plasma processing system 500 canbe similar to the embodiment of FIG. 3 or FIG. 4, and can furthercomprise an RF generator 570 configured to couple RF power to upperelectrode 352 through an optional impedance match network 572. A typicalfrequency for the application of RF power to upper electrode 352 canrange from about 0.1 MHz to about 200 MHz. Additionally, a typicalfrequency for the application of power to the substrate holder 320 (orlower electrode) can range from about 0.1 MHz to about 100 MHz. Forexample, the RF frequency coupled to the upper electrode 352 can berelatively higher than the RF frequency coupled to the substrate holder20. Optionally, the RF power to the upper electrode 352 from RFgenerator 570 can be amplitude modulated, or the RF power to thesubstrate holder 320 from RF generator 340 can be amplitude modulated,or both RF powers can be amplitude modulated. Desirably, the RF power atthe higher RF frequency is amplitude modulated. Moreover, controller 590is coupled to RF generator 570 and impedance match network 572 in orderto control the application of RF power to upper electrode 352. Thedesign and implementation of an upper electrode is well known to thoseskilled in the art.

Referring still to FIG. 6, the optional DC power supply 350 may bedirectly coupled to upper electrode 352, or it may be coupled toimpedance match network 572 to upper electrode 352. An electrical filtermay be utilized to de-couple RF power from DC power supply 350.

In the embodiment shown in FIG. 7, the plasma processing system 600 can,for example, be similar to the embodiments of FIGS. 3, 4 and 5, and canfurther comprise an inductive coil 680 to which RF power is coupled viaRF generator 682 through an optional impedance match network 684. RFpower is inductively coupled from inductive coil 680 through adielectric window (not shown) to plasma processing region 315. A typicalfrequency for the application of RF power to the inductive coil 680 canrange from about 10 MHz to about 100 MHz. Similarly, a typical frequencyfor the application of power to the chuck electrode can range from about0.1 MHz to about 100 MHz. In addition, a slotted Faraday shield (notshown) can be employed to reduce capacitive coupling between theinductive coil 680 and plasma. Moreover, controller 690 is coupled to RFgenerator 682 and impedance match network 684 in order to control theapplication of power to inductive coil 680. In an alternate embodiment,inductive coil 680 can be a “spiral” coil or “pancake” coil incommunication with the plasma processing region 315 from above as in atransformer coupled plasma (TCP) reactor. The design and implementationof an inductively coupled plasma (ICP) source, or transformer coupledplasma (TCP) source, is well known to those skilled in the art.

Alternately, the plasma can be formed using electron cyclotron resonance(ECR). In yet another embodiment, the plasma is formed from thelaunching of a Helicon wave. In yet another embodiment, the plasma isformed from a propagating surface wave. Each plasma source describedabove is well known to those skilled in the art.

In the embodiment shown in FIG. 8, the plasma processing system 700 can,for example, be similar to the embodiments of FIGS. 3, 4 and 5, and canfurther comprise a second RF generator 744 configured to couple RF powerto substrate holder 320 through another optional impedance match network746. A typical frequency for the application of RF power to substrateholder 320 can range from about 0.1 MHz to about 200 MHz for either thefirst RF generator 340 or the second RF generator 744 or both. The RFfrequency for the second RF generator 744 can be relatively greater thanthe RF frequency for the first RF generator 744. Furthermore, the RFpower to the substrate holder 320 from RF generator 340 can be amplitudemodulated, or the RF power to the substrate holder 320 from RF generator744 can be amplitude modulated, or both RF powers can be amplitudemodulated. Desirably, the RF power at the higher RF frequency isamplitude modulated. Moreover, controller 790 is coupled to the secondRF generator 744 and impedance match network 746 in order to control theapplication of RF power to substrate holder 320. The design andimplementation of an RF system for a substrate holder is well known tothose skilled in the art.

In the following discussion, a method of etching a thin film utilizing aplasma processing system is presented. For example, the plasmaprocessing system can comprise various elements, such as described inFIGS. 2 through 8, and combinations thereof.

FIG. 9 presents a flow chart of a method for etching a thin film using aplasma processing system according to an embodiment of the presentinvention. Procedure 900 begins at 910 with disposing a substrate on asubstrate holder in a plasma processing system configured to form aprocessing plasma.

In 920, the processing plasma is formed in a process space proximate thesubstrate by coupling electrical power, such as RF power, to a processgas introduced to the plasma processing system. The plasma generationsystem may include any known device configured to generate plasma, suchas those described above and in FIG. 4 through FIG. 8.

In 930, electrical power is coupled to an exhaust assembly. The exhaustassembly is disposed within the plasma processing chamber and configuredto surround the substrate holder. The exhaust assembly separates theprocess space from a pumping space coupled to a vacuum pumping systembelow the exhaust assembly. Electrical power can include DC power or ACpower, such as RF power. In 940, secondary plasma is formed beyond aperipheral edge of the substrate holder using the exhaust assembly inorder to alter the processing plasma by, for example, reducing theleakage of the processing plasma to the vacuum pumping system. Theexhaust assembly can include either embodiment presented in FIGS. 2 and3.

In 950, the substrate is exposed to the altered processing plasma inorder to, for example, etch one or more features on the substrate.

Although only certain embodiments of this invention have been describedin detail above, those skilled in the art will readily appreciate thatmany modifications are possible in the embodiments without materiallydeparting from the novel teachings and advantages of this invention.Accordingly, all such modifications are intended to be included withinthe scope of this invention.

1. A plasma processing system configured to process a substrate withplasma, comprising: a plasma processing chamber configured to facilitatethe formation of a processing plasma; a substrate holder coupled to saidplasma processing chamber and configured to support said substrate; aplasma generation system coupled to said plasma processing chamber andconfigured to form said processing plasma from a process gas in aprocess space adjacent said substrate; a vacuum pumping system coupledto said plasma processing chamber and configured to evacuate saidprocess gas; an exhaust assembly coupled to said plasma processingchamber around said substrate holder and separating said process spacefrom a pumping space coupled to said vacuum pumping system; and anelectrical power source coupled to said exhaust assembly and configuredto form a secondary plasma in order to alter said processing plasma. 2.The system of claim 1, wherein said exhaust assembly is configured toimprove the spatial uniformity of said processing plasma.
 3. The plasmaprocessing system of claim 1, wherein said exhaust assembly comprises: afirst exhaust plate surrounding said substrate holder, said firstexhaust plate having a plurality of openings to allow passage of processgas there-through; electrical insulation members coupled to said firstexhaust plate and configured to insulate said first exhaust plate fromsaid substrate holder and said plasma processing chamber; and a secondexhaust plate surrounding said substrate holder, parallel with saidfirst exhaust plate and below said first exhaust plate, said secondexhaust plate having a plurality of openings to allow passage of processgas there-through; said first exhaust plate being coupled to saidelectrical power source and said second exhaust plate being coupled toelectrical ground; and said secondary plasma being formed between saidfirst exhaust plate and said second exhaust plate during coupling ofelectrical power to said first exhaust plate.
 4. The plasma processingsystem of claim 3, wherein said first exhaust plate is fabricated fromaluminum has at least one surface thereon that is anodized or coated. 5.The plasma processing system of claim 4, wherein said at least onesurface of said first exhaust plate is coated with aluminum oxide oryttrium oxide.
 6. The plasma processing system of claim 3, wherein saidsecond exhaust plate is fabricated from aluminum and has at least onesurface thereon that is anodized or coated.
 7. The plasma processingsystem of claim 6, wherein said at least one surface of said secondexhaust plate is coated with aluminum oxide or yttrium oxide.
 8. Theplasma processing system of claim 1, wherein said exhaust assemblycomprises: a first exhaust plate surrounding said substrate holder, saidfirst exhaust plate having a plurality of openings to allow passage ofprocess gas there-through; electrical insulation members coupled to saidfirst exhaust plate and configured to insulate said first exhaust platefrom said substrate holder and said plasma processing chamber; and aground electrode coupled to an outer wall of said plasma processingchamber, perpendicular with said first exhaust plate and above saidfirst exhaust plate; said first exhaust plate being coupled to anelectrical power source and said ground electrode being coupled toelectrical ground, and said secondary plasma being formed between saidfirst exhaust plate and said ground electrode during coupling ofelectrical power to said first exhaust plate.
 9. The plasma processingsystem of claim 8, wherein said exhaust assembly further comprises: asecond exhaust plate surrounding said substrate holder, parallel withsaid first exhaust plate and immediately below said first exhaust plate,said second exhaust plate having a plurality of openings to allowpassage of process gas there-through.
 10. The plasma processing systemof claim 9, wherein said second exhaust plate is fabricated from anon-conductive material.
 11. The plasma processing system of claim 9,wherein said second exhaust plate is fabricated from one or more ofquartz, sapphire, silicon, silicon nitride, silicon carbide, alumina,aluminum nitride, Teflon®, or polyimide, or a combination of two or morethereof.
 12. The plasma processing system of claim 1, wherein saidplasma generation system comprises a capacitively coupled plasma (CCP)system, an inductively coupled plasma (ICP) system, a transformercoupled plasma (TCP) system, an electron cyclotron resonance (ECR)plasma system, a helicon wave plasma system, a surface wave plasmasystem, or a slotted plane antenna (SPA) plasma system, or a combinationof two or more thereof.
 13. The plasma processing system of claim 1,wherein said electrical power source comprises a DC power source or anAC power source or both.
 14. The plasma processing system of claim 1,wherein said electrical power source comprises a RF power source. 15.The plasma processing system of claim 1, further comprising: acontroller programmed to control the plasma processing system bycontrolling the coupling of electrical power to the exhaust assembly toform a secondary plasma to alter said processing plasma so as to improvethe spatial uniformity thereof.
 16. The plasma processing system ofclaim 1, further comprising: a controller programmed to control theplasma processing system to perform the following steps: disposing asubstrate on the substrate holder in the plasma processing chamber;forming a processing plasma in a process space above and adjacent thesubstrate disposed on the substrate holder in the plasma processingchamber using the plasma generation system coupled to said plasmaprocessing chamber; coupling electrical power to the exhaust assemblywithin said plasma processing chamber that substantially surrounds saidsubstrate holder and separates said process space from a pumping spacecoupled to the vacuum pumping system, thereby forming a secondary plasmain order to alter said processing plasma to thereby expose saidsubstrate to said altered processing plasma.
 17. The plasma processingsystem of claim 16 wherein said exhaust assembly comprises: a firstexhaust plate surrounding said substrate holder, said first exhaustplate having a plurality of openings to allow passage of process gasthere-through; electrical insulation members coupled to said firstexhaust plate and configured to insulate said first exhaust plate fromsaid substrate holder and said plasma processing chamber; a secondexhaust plate surrounding said substrate holder, parallel with saidfirst exhaust plate and below said first exhaust plate, said secondexhaust plate having a plurality of openings to allow passage of processgas there-through; and said controller is programmed to control theplasma processing system to couple electrical power between the firstexhaust plate and a ground electrode that is coupled to an electricalground, and forming the secondary plasma between the first exhaust plateand the ground electrode.